This invention relates to catheters used for detecting physiologic signals or used for therapeutic functions.
Many catheters used to detect physiological signals must be maintained in intimate contact with a physiologic member or tissue section in order to accurately and reliably detect a signal to measure a physiological parameter or deliver a therapy from or through the surface of the skin, mucosal membrane or vessel wall. Such catheters may, for example, include INTRA UTERINE CATHETERS, pulse oximetry sensors, ECG sensors, temperature or blood pressure sensors, used for measuring ECGs, oxygen tension, pH, oxygen saturation, biochemical analysis of skin and/or skin secretions, surface or skin temperature, blood pressure and the like.
Such devices generally include a sensing element and a mechanism for holding the element in pressure engagement with the member or tissue. When such sensors are held in position there is a possibility of tissue damage, patient discomfort or undesirable physiological reflex response to the applied pressure which may cause damage to surrounding or underlying tissue, measurement artifact and/or a reduction in quality of the signal acquired from the skin or tissue surface. For example, in reflection pulse oximetry, excessive sensor pressure can cause local exsanguination of blood from the underlying tissue structure, changing the optical absorption characteristics and thus introducing errors into the oxygen saturation calculated from the optical signals detected after transmission through the tissue section. Similarly, a sensor mounted on a rectal, fecal or esophageal catheter is required to be maintained in place without overextending the surrounding tissue and causing damage.
Another type of catheter is intended to be positioned in a body opening such as the cervix or esophagus for the delivering of a fluid or other therapy. Such catheters may also be positioned by a balloon in the uterus, at the cervical opening, for the purpose of inducing labor, delaying delivery or withdrawing amniotic fluid. Another use of balloon catheters is to block the esophagus during surgery to prevent the contents of the patient's stomach from being aspirated into the lungs. In these types of catheters, it is highly desirable to prevent excessive pressure in the balloon from overextending and possibly damaging tissue or underlying organs.